This method for inhibiting corrosion has special application to aqueous systems containing one or more of the following metallic materials: aluminum, copper, iron, and their respective alloys. The invention was developed in response to a need for maintaining recirculating 20% water-methanol solutions in a relatively corrosion-free and aseptic condition for extended periods. A 20% methanol-water solution had been selected as the heat-exchange medium for use in two types of experimental demonstration houses: a solar-heated house and a so-called ACES house heated and cooled by means of an Annual Cycle Energy System (The ORNL Review, fall issue, 1975, Oak Ridge National Laboratory, Oak Ridge, Tennessee). However, experiments conducted in closed systems demonstrated that when various metallic components were exposed to recirculating methanol/tap-water solutions for relatively short periods, the components corroded to such a degree that satisfactory long-term operation could not be expected. Aluminum-alloy components, such as heat exchangers and solar-heat-absorption panels, were found to be especially vulnerable to attack.
Tests established that the corrosion was caused both by chemical agents and the action of microorganisms (e.g., bacteria). As a specific illustration, a heat exchanger composed of Type 1100 aluminum alloy was exposed to recirculating 20% methanol-water (potable tap water) solution; within a month the exchanger developed pinholes. In another test conducted with the same type of solution, anaerobic bacteria in the closed system multiplied to the extent that the system became dangerously septic, exhibiting bacterial counts as high as 10,000,000 per milliliter. Bacterial action destroyed an aluminum-alloy screen in the system.